Enhancing Teredo IPv6 tunneling to traverse the symmetric NAT

By tunneling IPv6 packets over IPv4 UDP, Teredo supports IPv4/IPv6 dual-stack nodes in private IPv4 networks behind network address translation (NAT) to access IPv6 networks. However, the current Teredo protocol does not work with symmetric NAT. This letter proposes SymTeredo, an extension of Teredo with capability to traverse the symmetric NAT. Our extension preserves the Teredo architecture, and offers backward compatibility with the original Teredo protocol.